Mass spectrometers



July 25, 1961 R. D. CRAIG MASS SPECTROMETERS 7 Sheets-Sheet 1 Filed Jan. 19, 1960 INVENTOR ROBERT DEREK CRAIG '7 Sheets-Sheet 2 Filed Jan. 19, 1960 INVENTOR ROBERT DEREK CRAIG erd July 25, 1961 R. D. CRAIG MASS SPECTROMETERS 7 Sheets-Sheet 3 Filed Jan. 19, 1960 INVENTOR ROBERT DEREK CRAIG July 25, 1961 R. D. CRAIG MASS SPECTROMETERS 7 Sheets-Sheet 4 Filed Jan. 19, 1960 INVENTOR ROBERT DEREK CRAIG July 25, 1961 R. D. CRAIG 2,993,992

MASS SPECTROMETERS Filed Jan. 19, 1960 7 Sheets-Sheet 5 INVENTOR ROBERT DEREK CRAIG y 1961 R. D. CRAIG 2,993,992

MASS SPECTROMETERS Filed Jan. 19, 1960 7 Sheets-Sheet s INVENTOR ROBERT DEREK CRAIG July 25, 1961 R. D. CRAIG MASS SPECTROMETERS 7 Sheets-Sheet 7 Filed Jan. 19, 1960 INVENTOR ROBERT DEREK CRAIG United States Patent Ofiice Patented July 25, 1961 2,993,992 MASS SPECTROMETERS Robert Derek Craig, Altrincham, England, assignor to Associated Electrical Industries Limited, London, England, a company of Great Britain Filed Jan. 19, 1960, Ser. No. 3,428 Claims priority, application Great Britain Jan. 23, 1959 2 Claims. (Cl. 250-419) be diiferent.

If the ions are passed into a magnetic field, they will be deflected by an amount in accordance with their respective masses and in accordance with the strength of the magnetic field. If the ion beam is passed through a uniform magnetic field with suitably chosen boundaries, it will be dispersed into a mass spectrum. The resultant dispersed beam may be collected by a suitable collector, and since the ions of different masses will be separated, the constituent elements of the material can be readily determined.

A convenient way of receiving and recording and analysing the dispersed beam is by the use of a photographic plate or film. If such a plate or film, coated with a suitable sensitive emulsion, is placed in the path of the dispersed ions, the ions of different masses will appear as separated lines on the developed emulsion, the intensity and position of each line relative to a predetermined datum indicating respectively the quantity and the mass of each type of ion present in the material. By varying the time of exposure, it is possible to determine the types of the ions which appear in the greatest concentration, and also the ions that appear in the smallest concentration, as well as the diiferent types of ions in between these two extremes.

The magnetic analyser, which is taken to include the pole pieces between which the magnetic field is formed and the holder for the photographic plate, is evacuated during the operation of the spectrometer and therefore each time a photographic plate is required to be replaced it would normally be necessary to open up the magnetic analyser, thus destroying the vacuum, replace the plate, re-seal the analyser, and re-evacuate the complete analyser. Such a process is lengthy and undesirable.

The object of the present invention is to provide a magnetic analyser for a mass spectrometer which avoids the necessity for destroying the vacuum in the analyser each time the photographic plate is replaced.

According to the present invention, a magnetic analyser for amass spectrometer comprises a chamber, means for producing a magnetic field in said chamber, means for evacuating said chamber, a holder for a photographic plate or film within said chamber, a magazine connected in .agas-tight manner to said chamber, a carrier in said magazine for a plurality of photographic plates, means for moving said carrier so that each of'said photographic plates in turn is moved into a loading position within said magazine and means for transferringeach of said photographic plates in turn from said loading position to said, holder, the arrangement being such that ifan ion beam from an ion source is projected into said magnetic field, the beam will be dispersed into end walls 22 and 23. aperture 24. The end wall 22 is attached to a cylindri- 2 a spectrum which will impinge upon the photographic plate which is in the holder.

Preferably the chamber comprises means for moving the holder laterally so that different portions of each photographic plate or film may be exposed successively to the ion beam.

A valve may be provided between the magazine and the chamber so that the magazine can be removed without destroying the vacuum in the chamber.

In order that the invention may be more readily understood, reference will now be made to the accompanying drawings in which:

FIG. 1 is a side view, sectioned on a plane through the axis, of the part of a magnetic analyser in which a magnetic field is produced.

FIG. 2 is an end view of the apparatus illustrated in FIG. 1 sectioned in the plane II--H,

FIG. 3 is a side view, sectioned on a plane through the axis, of a magazine including a carrier for photographic plates,

FIG. 4 is an end view of the magazine illustrated in FIG. 3,

FIG. 5 is an end view of the magazine sectioned on a plane VV in FIG. 3,

FIG. 6 is an exploded view of a light tight cassette for a photographic plate or film,

FIG. 7 is a perspective view sectioned on a longitudinal plane of a cassette, and

FIG. 8 is a diagrammatic view of a mass spectrometer including a magnetic analyser embodying the invention.

Reference will also be made to FIG. 9 of the accompanying drawing which is an end view, in section, of a modified form of the part of the magnetic analyser illustrated in FIGS. 1 and 2.

With reference to FIGS. 1 and 2 a magnetic field is formed in a chamber 1 between the faces of the two magnetic pole pieces 2 and 3 which extend laterally across the chamber towards one another and are separated by .a gap 4. The pole pieces are included in a magnetic circuit which includes a yoke 5 and a base member 6, portions of which are illustrated in FIG. 2. The side walls 7 and 8 of the chamber 1 are also formed from magnet isable material. An aperture 9 is formed in one end wall of the chamber and this aperture is adapted to be connected to an ion source, which may be of the type described in co-pending patent application Serial No. 3,426 of January 19, 1960, of Craig. An electrostatic analyser, such as the type described in co-pending patent application Serial No. 3,427 of January 19, 1960, of Craig, maybe connected between the ion source and the aperture 9. The ion source produces a beam of ions which enters'the gap 4 and is deflected to form a spectrum as described above. The ions are arranged to be deflected upwards towards a holder 11 for a photographic plate. The chamber -1 is adapted to be evacuated by means of a pump 12 through an aperture 13 in one end wall. The chamber is supported from the base member 6 by suitable supports 14 and 15, which may have a small area of contact withthe surface of the chamber so as to .a magazine 17. The magazine 17 is adaptedto holda plurality ofphotographic plates.

The construction of the magazine 17 will now be described with reference to FIGS. 3, 4 and 5. The magazine comprises a cylindrical container 21 formed with In the end wall 22 is formed an cal member 25 having two transversely extending walls 26, 27. Apertures 28 and 29 are formed respectively in the end walls.

the walls 26, 27. The wall 27 connects with the end wall of chamber 1 and the aperture 29 communicates with the aperture 16 in the end wall of the chamber 1. The aperture 28 is adapted to be closed in a gas-tight manner by a flap valve 31, which is hinged on a shaft 32 and is operated from outside the magazine. Suitable sealing rings are provided between the mating faces. The aperture 29 is adapted to be closed in a gas-tight manner by means of a sliding valve 33 which is controlled by an arm 34 and moves in a cage 35. Suitable scaling is provided by having the mating surfaces polished optically flat and the valve is operated from outside the magazine 17. The second end wall 23 of the magazine is formed with an aperture 36 and this is adapted to be closed by a flap valve 37 hinged at 38. Suitable sealing rings are provided between the mating faces.

A drum 41 mounted on a spindle 42 extends longitudinally within the magazine. The spindle 42 is sup ported in a bearing 43 on the end wall 22 and extends in a gas-tight manner through a bearing 44 in the end wall 23 and terminates in a knob 45. The drum 41 is formed with end walls 46, 47 and bars 50 which extend between The end walls are octagonal in shape and each side of the drum is adapted to hold a light tight cassette 51. One cassette 51 is illustrated in FIGS. 6 and 7. Pins 48 are formed extending from the inner face of the end wall 46 and these are adapted to fit into co-operating holders in the bodies of the cassettes so as to retain one end of each cassette in position. Spring clips 49 are attached to the outer face of the end wall 47 and are adapted to engage With flanges on the cassette and retain them in position on the sides of the drum 41. The drum 41 may be rotated by means of the knob 45 and a spring loaded ball 52, co-operating in turn with holes 53 dispersed about the end wall 46, enables the drum to be stopped in any one of eight positions, thus enabling any one of the eight cassettes to be positioned in turn at the top of the drum.

Each cassette is formed with a lug 54. A rod 55 slides longitudinally on suitable supports within the magazine and extends in a gas-tight manner through the flap 37 and through a plate 56, terminating in a knob 57. The plate 56 is attached to two guide rods 58, 59 which extend longitudinally outside the magazine in guides 61, 62. The

plate 56 is formed with a handle 60 and may be moved longitudinally away from the magazine, so as to move the rod 55 longitudinally within the magazine. The inner end of the rod 55 is formed with a radial projection 63 which is adapted to engage with the lug 54in the end of the cassette when it is suitably positioned. The rod 55 may be rotated by the knob 57 between two positions regulated by a projection 64 on the knob which engages with a stop 65 on the face of the plate'56. If the plate 56 is moved so that the rod 58 extends fully within the magazine, the projection 63 will be located between the lug 54 and the end wall 23. By rotating the rod 55 the projection 63 can be located directly behind the lug and if the rod 55 is then moved back into the magazine, the projection 63 will engage with the lug 54 and the sliding portion of the cassette (see FIGS. 6 and 7) will 6 move longitudinally. If the valves 31 and 33 are opened, the rod 55 and the sliding portion of the cassette, which holds the photographic plate, will pass into the chamber 1 and will be supported in the holder 11. The sliding portion of the cassette is pushed into the chamber until it abuts against a projection 66 on the top of the pole pieces 2, 3. The rod 55 can then be withdrawn so as to allow the valve 33 to be closed. To remove the sliding portion of the cassette, the rod 55 is rotated so that the projection 67 is no longer aligned with the lug 54. The rod is then pushed into the chamber until the projection 63 passes the lug 54, the rod is rotated until the projection 63 is located behind the lug 54 and on the remote side thereof and the rod is then moved outwardly bringing the sliding portion of the cassette with it. The slid- 4 ing portion ofthe cassette is thereby returned to the fixed portion of the cassette which is still in position on the upper side of the drum 41.

The construction of the cassette 51 is illustrated in FIGS. 6 and 7. The cassette comprises a fixed portion and a sliding portion. The fixed portion is formed from a first plate 71, to one end of which is attached a rectangular socket 72 and the other end of which is tapered at 73. A second plate 74 is attached to one surface of the first plate 71 and a third plate 75 is attached to the outer face of the plate 74. The ends of the third plate 75 are bent so as to form flanges 76 and 77. These flanges may be reinforced if required, by suitable webs. The plates 71, 74 and 75 are drilled before assembly so that a path for gas extends from the outer surface of the plate 75 to the outer surface of the plate 71, and so arranged that this path is light-tight. This path is therefore conveniently formed in a zig-zag formation in the middle plate 74. The outer aperture of this path is shown at 78. The flange 76 is formed with holes 81, 82 which are adapted to receive the pins 48 on the inner face of the end wall 46 of the drum 41, and these pins locate one end of the casette in position. The second flange 77 is formed with a hole 83, and this flange engages with the spring loaded clip 49 and a suitable pin on the second end of the wall 47 of the drum. This flange is retained in position by the spring clip and the combined action of the clip and the pins retains the cassette rigidly in position on the drum.

The sliding portion of the cassette consists of a plate 84, three edges of which are formed with channel members 85, 86, and 87. The sliding portion fits over the plate 71, the edges of the plate 71 engaging with the grooves formed by the channel members 85, 86 and 87. One end of the plate 84 is received by the rectangular socket 72 and hence a light-tight container is formed between the plates 71 and 84. The sensitised photographic plate is attached to the inner surface of the plate 84 and is conveniently a push tight fit in the grooves formed by the channel members 85, 86 and 87. The lug 54 is attached to the outer surface of the plate 84. When the projection 63 on the rod 55 engages with the lug 54, the sliding portion of the cassette moves off the fixed portion, carrying a photographic plate with it. The photographic plate is therefore transferred from the cassette to the holder 11.

The holder 11 is formed with two supporting guide members 105, 106 supported from frames 107, 108 which are joined by a rod 94. These frames are supported by two rods 89, 91 which extend transversely across the chamber and are supported by a framework 92 which is attached to the top 93 of the chamber. The frames 107, 108 are thus able to move laterally across the chamber. The guide members 105, 106 are adapted to support the sliding portion of the casette and hence the sliding portion of the cassette, and the photographic plate contained therein, can be moved laterally across the chamber. This action permits different portions of the photographic plate to be located above the gap 4 between the pole pieces and hence to be exposed to the ion spectrum. The rod 94 joining the frames 107, 108 is moved laterally by a fork 96 located at the lower end of a rod 95. This fork engages each side of the rod 94. The rod extends upwards, is rotatable about an axis 97 and extends outside the chamber through a bellows 98 to a gear mechanism 99. The gear mechanism 99 controls the lateral movement of the upper end of the rod 95. This movement also moves the fork 96 laterally and hence the sliding portion of the cassette may be moved laterally as required.

FIG. 8 is a diagrammatic view of a mass spectrometer which includes a magnetic analyser as described above.

With reference to FIG. 8, the ion source 10 is connected to one end of the chamber 1, in which the magnetic field is produced. The chamber 1 is adapted to be evacuated by the pump 12. The magazine 17, containing the photographic plates, is connected to the chamber 1 by means of the cylindrical member 25. A pump 101 is connected to the member 25, and a further pump 102 is connected through a valve 103 to the magazine 17.

The operation of the mass spectrometer is as follows. The material which is to be analysed is placed in the ion source, the ion source is sealed and is attached to the chamber 1. The drum 41 in the magazine is loaded with cassettes containing photographic plates. The magazine is closed and sealed in a gas-tight manner and with the valves 31 and 33 closed is evacuated by means of the pump 102. When a fairly low pressure is reached, the valve 103 is closed, valve 31 is opened and the magazine is further evacuated by pump 101. It will be noted that while the cassettes are in the magazine they will be evacuated by way of the light tight path formed through the plates 71, 74 and 75 in the fixed portion of each cassette. When it is required to analyse the material, valve 33 is opened, the rod 55 is withdrawn, is rotated so that the projection 63 engages with the lug 54 on the cassette in the top position in the drum, and is pushed back again into the magazine so that the sliding portion of the cassette is transferred to the holder 11 within the chamber 1. The holder 11 must be correctly aligned with the cassette before the transfer is commenced. This operation is performed without aifecting the vacuum in the chamber 1. A beam of ions is then projected from the ion source into the magnetic field in the chamber 1 and the spectrum of ions so formed will impinge upon the photographic plate. Several exposures can be made on the plate and it may be moved laterally between each exposure. When the plate is fully exposed, the rod 55 is used to withdraw the sliding portion of the cassette back into the fixed position. The holder 11 must be correctly aligned with the rod before the transfer commences. The drum 41 is then rotated until the next cassette is in the top position on the drum and the sliding portion of the next cassette can then be inserted in the chamber and more exposures can be made.

When all the photographic plates have been exposed, the valves 31, 33 are closed and the magazine 17 is opened by means of the flap 37. The cassettes can then be replaced. When the magazine is resealed, it will, of course, have to be re-evacuated by means of the pumps 101, 102 before the mass spectrometer can be operated again.

The magnetic analyser described above enables several exposures to be made of a photographic plate and enables the photographic plate to be replaced by a fresh plate without destroying the vacuum within the mass spectrometer. By storing several photographic plates within the magazine, it is possible to evacuate the cassette before use and a large number of exposures can be obtained without the necessity for re-evacuating the mass spectrometer.

An alternative construction of the chamber 1 is shown in FIG. 9. The pole piece assembly comprising the two pole pieces 2, 3 and suitable non-magnetic spacers 115, 116 is supported from top and bottom walls of chamber 1 by means of suitable supports 111, 112, 113 and 114. The side walls 7, 8 may then be welded around their edges to the top and bottom walls of chamber 1 and are preferably made thin so that they may be made from the same non-magnetic material as the chamber 1.

What I claim is:

1. A magnetic analyser for a mass spectrometer com prising a chamber, means for producing a magnetic field within said chamber, means for evacuating said chamber, a holder for a photographic plate within said chamber, a magazine connected in a gas tight manner to said chamber, a drum within said magazine, means for rotating said drum, means for securing a plurality of cassettes for said photographic plates to the periphery of said drum so that each cassette is moved in turn into a loading position when said drum is rotated, and a rod adapted to move longitudinally relative to said drum and to transfer each photographic plate in turn from the corresponding cassette when it is in the loading position to said holder within said chamber, the arrangement being such that if an ion beam from an ion source is projected into said magnetic field, the beam will be dispersed into a spectrum which will impinge upon the photographic plate which is in the holder.

2. A magnetic analyzer for a mass spectrometer comprising a chamber, means for producing a magnetic field within said chamber, means for evacuating said chamber, a holder for a photographic pl-ate within said chamber, a magazine connected by a valve to said chamber, means for evacuating said magazine, a drum within said magazine, means for rotating said drum, means for securing a plurality of cassettes for said photographic plates to the periphery of said drum so that each cassette is moved in turn into a loading position when said drum is rotated, and a rod adapted to move longitudinally relative to said drum and to transfer each photographic plate in turn from the corresponding cassette when it is in the loading position to said holder within said chamber, the arrangement being such that if an ion beam from an ion source is projected into said magnetic field, the beam will be dispersed into a spectrum which will impinge upon the photographic plate which is in the holder.

References Cited in the file of this patent UNITED STATES PATENTS 2,483,872 Bensen Oct. 4, 1949 2,622,204 Shaw Dec. 16, 1952 2,857,521 Moscatelli Oct. 21, 1958 

